Burglar alarm



April 1970 J. v. FONTAINE 7 3,508,239

BURGLAR ALARM Filed March 15, 1967 v UU- INVENTOR JOHN V. FONTAINE ATTORNEY United States Patent US. Cl. 340258 4 Claims ABSTRACT OF THE DISCLOSURE An electronic alarm and warning device including a transistor oscillator connected to a current source, a tuned coil in circuit with the transistor oscillator and tuned in accordance with the frequency of the oscillator to develop a predetermined voltage, a door knob sensor connected to the tuned coil, a silicon controlled switch connected to the tuned coil so that the predetermined voltage is insufficient to fire the switch but a change in voltage produced when a person touches or closely approaches the door knob sensor is suflicient to fire the silicon controlled switch, and an alarm signal means actuated in response to firing of the silicon controlled switch to provide a signal. The alarm signal means preferably includes a relay energized by conduction of the silicon controlled switch to in turn energize a lamp providing a warning signal. Also included in the alarm signal means is an audible alarm device connected to a second silicon controlled switch which is fired only if another change of voltage at the tuned coil occurs after a predetermined delay set by a timer.

This invention relates to alarms, signals or warnings devices and more particularly to an arrangement by which a visual or an audible signals or both, can be set in operation by the close proximity of the body of a human being to a sensory element forming a part of the circuit for the It is an object of the invention to provide a warning signal or alarm which will be positive in operation; which will not be affected by any fluctuation or power surges in the voltage supply circuit, and which will operate on a sensor that is almost totally grounded.

An important object of this invention is the ability of the device to frighten a high percentage of prowlers away before entry and without disturbing the occupants unless the would-be prowler persists and only then will the alarm sound alerting the occupant to take appropriate action.

A further object of the invention is to provide a capacity reactor that is activated by a pulse only rather than through an increase in voltage or a discharge.

The advantages of a pulse activated unit are:

(A) It can be connected to a partially grounded object and still operate satisfactory.

(B) It is not effected by fluctuations in the supply voltage which usually cause false alarms or render the unit inoperable.

With these and other objetcs to be hereinafter set forth in view, I have devised an arrangement of parts to be described and more particularly pointed out in the claims appended hereto.

In the accompanying drawing forming a part hereof is shown the schematic wiring diagram of the improved signal device or alarm.

Therein the plug shown at 1 is connected into a conventional power outlet and has its lead wires 2 and 3 extended to a stepdown transformer 4. A switch 5 is incorporated in the lead wire 3. The transformer 4 connects to a silicon rectifier 6 from which a wire 7 extends, with interposed resistor 9, to an oscillator unit generally indicated at 10.

From the oscillator 10 there is extended a wire 11 leading to a discriminator coil shown at 12, and a capacitor being interposed in the lead wire 11 as shown at 13. The discriminator coil 12 is connected to a sensory element or antenna 14. Such elements may be any suitable metallic member such as a door knob, window or door screen, railing around a swimming pool or any other suitable element by means of which a reaction is obtained when a person approaches closely to it or touches it.

Discriminator coil 12 is also connected to diode 18. The positive side of diode 18 is connected to meter 15 and silicon control switches 19 and 25.

19 is a silicon control switch that is connected in series with normally open relay 24 and through the normally closed points 20' of bimetal switch 23.

A silicon control switch 25 is connected in series with bell 17 and through normally open points 16 of bimetal switch 22.

Normally open points 20 of relay 24 are connected to light 21, and normally open points 26 of relay 24 are connected to heaters of delay relays 22 and 23.

The alarm works in the following manner.

The sensor element 14 is approached by a human. The frequency of discriminator coil 12 is changed causing a rapid change in voltage amounting to a pulse which is the only type of change that will activate the unit.

Upon the silicon control switch 19 receiving a pulse the normally open relay 24 closes. One set of its points 20 switches on light 21 and the other set of its points 26 activate two separate delay timers 22 and 23 simultaneously.

Timer 23 has a delay of two minues and has normally closed points 20'. After two minutes the points 20 will open causing realy 24 to deenergize and in turn switch off lights 21.

The second timer 22 has a two second normally open points 16 and after a two second delay points 16 colse completing a circuit which will allow a second pulse, if received, to activate silicon control switch 25 causing alarm 17 to sound.

In other words if 2 pulses are received with any more than a two second interval the alarm 17 will sound. If only one pulse is received only the light 21 will be switched on.

In either event the unit will shut off the light and alarm after a two minute interval and reset.

It will be apparent from the foregoing that by means of the arrangement discolsed there is provided a tuned oscillator and discriminator coil, the latter supplying voltage to silicon controlled switches which control a visual and audio operation of a signal device. The sensor, being connected to the discriminator coil, will change the frequency thereof on the approach or contact of a body with the sensor, and the switch being accordingly activated, will then cause the operation firstly of the visual and secondly of the audio signals.

The described arrangement has numerous advantages over known units, some of such advantages being due to the fact that the system will not be affected by surges and fluctuation of the power supply voltage; it can operate with its sensor or antenna alomst totally grounded; no radiation problems are involved and almost any metallic object of various size and lengths can be employed as the sensory element.

Another important advantage disclosed is a practical alarm system that frightens the burglar away before entry by turning on the lights. While still a further advantage is the ability to do the above without disturbing, in most instances, the occupant, while still sounding an alarm to arouse and warn the occupant if the would-be burglar persists and in either and all cases before the burglar has gained entry.

What I claim is: v

1. An electronic alarm comprising a current source a transistor oscillator connected to said current source, tuned coil means in circuit with said transistor oscillator, said coil means being tuned in accordance with the frequency of said oscillator to develop a predetermined voltage across said tuned coil means, a doorknob sensor connected to said tuned coil means adapted to be touched to produce a steep voltage pulse across said tuned coil means by changing the tuning thereof, a silicon controlled switch selectively responsive to a voltage pulse, said switch having an anode-cathode portion connected to said current source and having a gate connected in circuit with said tuned coil means so that said predetermined voltage is insuflicient to fire said switch but said voltage pulse selectively causes said switch to fire and thus become conductive, said silicon controlled switch being unresponsive to a "gradual voltage change, and alarm signal means actuated in response to firing of said silicon controlled switch to provide a signal upon firing thereof.

2. The electronic alarm as claimed in claim 1 in which said alarm signal means includes a relay having a coil connected in circuit with the anode-cathode portion of said switch, a lamp connected to said current source, and normally open contacts of said relay connected in circuit with said lamp to cause energization of said lamp upon closing of said contacts by energization of said coil upon conduction of said silicon controlled switch, said lamp providing a Warning signal.

3. The electronic alarm as claimed in claim 2 in which said alarm signal means further includes a second silicon controlled switch having an anode-cathode portion connected to said current source and a gate portion connected to said tunedcoil means, an-audible alarm device connected in circuit with said anode-cathode portion of said second switch, and a timer, said relay having contacts connected to said timer to actuate the same upon energization of said relay, and said timer having contacts connected in circuit with said alarm device to delay activation thereof for a predetermined time set by said timer so that only if another voltage change at said tuned coil means occurs after the period of said timer is said second silicon controlled switch fired to actuate said alarm device to sound an audible alarm.

4. The electronic alarm as claimed in claim 3 in which said alarm signal means further includes another timer connected in parallel with said first named timer and actuated therewith but having a longer timing period, said other timer having contacts connected to said relay coil to deenergize the same after a predetermined period of time to stop said warning signal and said audible alarm when in elfect.

References Cited UNITED STATES PATENTS 2,637,801 5/1953 Kelley et a1. 340--274X 3,129,414 4/ 1964 Rice. 3,329,838 7/1967 Myers. 3,355,709 11/1967 Hanus 340-171 JOHN W. CALDWELL, Primary Examiner -P. PALAN, Assistant Examiner US. Cl. X.R. 340-276 

